There is considerable evidence that some mercury from silver dental fillings distributes to body tissues, particularly the brain. Occupational exposure to mercury vapor is associated with an increased prevalence of neurological impairments and neuropsychological deficits, such as visuospatial ability, memory, attention, tremor, peripheral nerve function and balance, as well as increased reporting of subjective symptoms. This study will test whether exposure to lower levels of mercury vapor, namely those associated with dental amalgams, is associated with subtle neurological and neuropsychological effects. Specific aims are: 1)To determine whether amalgam-derived mercury exposure, as assessed by counts of total and occlusal amalgam surfaces is associated with a)neuropsychololgical deficits, b)neurological impairments and c)subjective symptom reporting. Visuomotor and visuospatial coordination, memory, attention, executive function, symptom reporting and postural sway will be measured by standardized test. Tremor, gait strength, and coordination will be measured by a structured clinical neurologic examination. 2)To investigate the above associations, using urinary mercury as an index of exposure. 3)To describe the determinants of urinary mercury concentration. Characteristics thought to be associated with inorganic mercury exposure concentration amalgams include the number and location of amalgam surfaces (total and occlusal), the time the amalgams have been in place, recent dental work, chewing habits and bruxism. We will examine whether these variables modify the relationship between amalgam counts and urinary mercury.